1 use std::env;
2 use std::process::Command;
3 use std::str::{self, FromStr};
4
5 // The rustc-cfg strings below are *not* public API. Please let us know by
6 // opening a GitHub issue if your build environment requires some way to enable
7 // these cfgs other than by executing our build script.
main()8 fn main() {
9 let minor = match rustc_minor_version() {
10 Some(minor) => minor,
11 None => return,
12 };
13
14 // #[track_caller] stabilized in Rust 1.46:
15 // https://blog.rust-lang.org/2020/08/27/Rust-1.46.0.html#track_caller
16 if minor >= 46 {
17 println!("cargo:rustc-cfg=track_caller");
18 }
19 }
20
rustc_minor_version() -> Option<u32>21 fn rustc_minor_version() -> Option<u32> {
22 let rustc = match env::var_os("RUSTC") {
23 Some(rustc) => rustc,
24 None => return None,
25 };
26
27 let output = match Command::new(rustc).arg("--version").output() {
28 Ok(output) => output,
29 Err(_) => return None,
30 };
31
32 let version = match str::from_utf8(&output.stdout) {
33 Ok(version) => version,
34 Err(_) => return None,
35 };
36
37 let mut pieces = version.split('.');
38 if pieces.next() != Some("rustc 1") {
39 return None;
40 }
41
42 let next = match pieces.next() {
43 Some(next) => next,
44 None => return None,
45 };
46
47 u32::from_str(next).ok()
48 }
49